Determination of climatic changes in the past is a means to predict what may happen in the future. There are several means to measure changes in past climate, one of which is the immense reservoir of information locked in preserved leaves. There are a huge number of plants preserved in herbaria around the world, including more than 1 million plants inthe Smithsonian US Herbarium.

Climate during the time of Lewis and Clark

In association with the Academy of Natural Sciences in Philadelphia, we used stable isotopes to determine climate conditions during the early 1800s. By examining the leaf tissue of plants collected by the Corps of Discovery, we showed that leaves could be used as a reliable indicator of past climates.